MONTREAUX, Switzerland (CNN) -- Some people will go to great lengths to hang on to their youth -- and if you have enough money, those lengths can involve being injected with a substance made from the liver of a lamb's fetus.

The "rejuvenation" treatment, which promises to slow down the aging process, is administered at the headquarters of Swiss top-end beauty company La Prairie.

Situated next to Lake Geneva, Clinique La Prairie opened in 1931.

Back then it was frequented by the rich and famous, including Charlie Chaplin, who was a regular of the treatment --subjecting himself to 16 large injections, into the buttocks, filled with the fresh cells from the fetus of a sheep.

The injections were crude and so painful that the recipients had to lie on their faces for three days while their swollen bottoms recovered.

Today, the premise is the same -- to slow down the aging process -- but the procedure is less rudimentary, though still not for the faint-hearted.

La Prairie stopped giving patients fresh, live cells a decade ago. These days, nurses administer the injections, which are filled with an extract made from fetal liver, harvested from specially reared black sheep.

Technicians prepare the elixir at a laboratory onsite, where they isolate the active "rejuvenating" chemicals from the organ of the unborn animal.

The extract is billed as a powerful booster for aging immune systems, flagging memories, and is also said to have cancer-fighting properties.

Dr. Thierry Walli, the clinic's chief physician, said that although the extract gets results, it does not promise eternal youth, which is impossible to achieve. It does, however, slow the aging process down, he said.

"Anti-aging treatments for me don't really exist, real ones. You don't stop aging. You can interfere a little bit with the life quality of aging people, but you don't stop."

The clinic also offers more conventional methods of fighting the aging process, including laser surgery, latest dermatology treatments, plastic surgery and even dental reconstructions.

But it is the use of unborn sheep organs that continues to attract, rather than dissuade, clients from all over the world.

Walli has the injections himself and is not bothered about criticism that the process is unethical.

"We know that with one fetal liver we can treat 25 to 30 people. So, if we treat a 1,000 people a year we need about 40 sheep babies. What is 40 sheep babies? That is more or less 20 sheep mothers. So, 20 sheep mothers in comparison to all the New Zealand sheep which are eaten in the world is just nothing," he said.

The treatment has achieved a cult following at the clinic, which is part five-star hotel, part medical unit and part beautician's parlor.

David Dafinone is an annual visitor to Clinique La Prairie, where he spends at least $20,000 for a week's "rejuvenation."

The 78-year-old told CNN he felt 40 years old, and put a lot of that down to the treatment.

"Price is relative. So, if you get satisfaction for the money that you paid then it was worth it. And paying even double I would still come here. It is good," Dafinone said.